Conventionally, aircraft brakes are controlled by a pilot by way of left and right foot brake pedals that provide independent control of brakes on the left and right hand sides of the aircraft. Any variation in overall braking performance on each side of the aircraft would result in the aircraft veering to one side of the runway. However, the pilot is able to use the independent brake controls for the left and right hand sides of the aircraft to compensate for any such variation and keep the aircraft stable and straight down the runway.
For UAVs the brake control system needs to assume the role of the pilot in keeping the aircraft travelling in a straight line during braking. A simple controller actuating all brakes to achieve a desired level of aircraft deceleration would not take into account variations in the torque generated by the brake units on the left and right hand sides of the aircraft. Any variation in brake torque between the two sides of the aircraft will result in the aircraft veering to the side of the runway corresponding to the side with the greatest brake torque.
Systems exist for controlling the pressure applied to brakes in response to signals representative of the applied brake torque. However, such systems rely on costly sensors and the control is difficult given the variation in torque that is seen with the carbon-carbon friction materials that are used in modern aircraft brakes.